Estimation of power output and conversion efficiency for quantum dot lasers

Interest in Quantum Dot Lasers stem mainly from the low threshold current which can result due to quantization of energy levels and change in density of state function. In the most used lasers, separate confinement heterostructures, the nanoscale active region is ‘built into’ the waveguide region (optical confinement layer, OCL) based on a wide gap semiconductor material.The most important characteristic of quantum dot laser is the amount of light it emits as current is injected into the device. The dependence of laser power output on current, cavity length, and various other parameters has been estimated based on the rate equations model. Linear relation has been obtained between power and current and as the cavity length increases, the slope of the power–current characteristic decreases.The external quantum efficiency indicates the efficiency of a laser device in converting the injected electron–hole pairs (input electric charges) to the photons emitted from the device (output light). External differential quantum efficiency decreases linearly with increasing cavity length. As the internal loss increases, the slope of external differential quantum efficiency versus cavity length increases. The internal quantum efficiency is independent of the geometrical properties of the laser device, such as the cavity length or the stripe width. Internal quantum efficiency is one of the main figures of merit that should be used in assessing the quality of the semiconductor wafer from which the quantum dot laser is manufactured.One of the most important device characteristics of a laser diode is the efficiency of conversion of the input electric power into output optical power. Power conversion efficiency is found to increase with increasing drive current, gets its maximum value and after that it decreases slightly with increasing drive current. Power conversion efficiency also depends on different parameters like cavity length, internal efficiency, and threshold current.